Merge i18n files, step 1

The stated reason for splitting, performance, is not valid at least since 1.16
so let's keep things simple.

Step 2: full export from Translatewiki will move the rest of messages into the same file.
Step 3: Delete the emptied file.

Change-Id: I7cdba22611f2948d09600fd08e52f1778f22c52d
Merge "Merge i18n files, step 1"